With the rapid development of computer, CAD has widely used in Part design and manufacturing，but because of the commonality of CAD software，it is difficult to meet the specific needs of variable product design, so on the basis of CAD software，according to the actual situation to carry out secondary development has become an important work of modern design.As an important engineering mechanical transmission apparatus,gears have a very wide application Potential because of its advantage，such as high stability and bearing loads. However，the structure of gears are very sophisticated，and design difficulties. To improve the design efficiency and increase the competitive capacity，it is very important to realize the 3-D parametric modeling of gears. This dissertation constructed an accurate parametric model of involutes spur gear using three-dimensional modeling based on Pro/E software. It systematically studied the process of building 3D parametric model by Pro/E in the dissertation. It can regenerate a new model of gear due to parametric model of gear changes correspondingly according to the change of drive Parameters. Therefore it avoids the repetitive tasks in modeling，thus improves the efficiency of analysis greatly and reduce the costs.